A three dimensional object can be built up one section at a time, that is layerwise. A planar layer of material is solidified in contact with the fabrication platform in the shape of a section through the object. Solidification is achieved by the application of radiation, such as electromagnetic radiation or an electron beam (“actinic radiation”). Once the section is formed, another is formed in contact with the previously formed section. Repetition of this process allows multi-laminate objects to be fabricated. This is the basis of additive fabrication techniques such as stereolithography and selective-laser-sintering.
The process requires the shaping member and the fabrication platform to be parallel and a known distance from each other. This ensures that layers of raw material, particularly the first several layers used to form an object, are of even thickness and not wedge shaped. Overly thick layers, or wedge shaped layers, may be too thick in some parts to cure throughout. Uncured layers may not attach to the fabrication platform. This may cause the fabrication process to fail.
The process also requires the shaping member and fabrication platform to be aligned to the apparatus, in particular, the radiation source. This ensures that layers of raw material are formed at the focal plane of the radiation source. Out-of-focus projection of the radiation source results in loss of fabrication tolerances and may cause the process to fail.
Known approaches to the alignment of critical components rely on dial-indicator tools or feeler gauges to measure spacing at several points. Known approaches may be iterative and error prone.